Position tracking system and method using radio signals and inertial sensing

Abstract

An RF position tracking system for wirelessly tracking the three-dimensional position of a tracked object. The tracked object has at least one mobile antenna and at least one inertial sensor. The system uses a plurality of base antennas which communicate with the mobile antenna using radio signals. The tracked object also incorporates the inertial sensor to improve position stability by allowing the system to compare position data from radio signals to data provided by the inertial sensor.

What is claimed is: 
     
       1. A mobile device comprising:
 multiple receiver antennae each configured to receive radiofrequency (RF) signals transmitted by at least one RF transmission source for determining a position of the mobile device; 
 a sensor configured to measure inertia of the mobile device; and 
 at least one processor in communication with the sensor and the at least one receiver antenna, the at least one processor being configured to:
 receive inertial measurement data measured by the sensor; 
 calculate, from position information of the RF signals, a first position of the mobile device; 
 compare the position information of the RF signals and the inertial measurement data to modify a position stability of the RF signals; and 
 calculate, from the inertial measurement data measured by the sensor and the calculated first position, a second position of the mobile device for tracking the mobile device, wherein the at least one processor is further configured to reduce power to the at least one receiver antenna when the sensor does not detect motion for a period. 
 
 
     
     
       2. The mobile device of  claim 1 , wherein the at least one processor is further configured to use a subsequent calculation of position information for the mobile device based on an inertial measurement as the position of the mobile device when the RF signals are weak, corrupted, or missing. 
     
     
       3. The mobile device of  claim 1 , wherein the at least one processor is further configured to apply a weight to the position information based on the inertial measurement in response to detecting a divergence between first and second position information of the position information. 
     
     
       4. The mobile device of  claim 1 , wherein the mobile device is an unmanned aerial vehicle. 
     
     
       5. The mobile device of  claim 1 , wherein the sensor comprises one or more accelerometers, zero or more gyroscopes, and zero or more magnetic sensors. 
     
     
       6. The mobile device of  claim 1 , wherein the at least one processor uses a Kalman filter to merge the position and orientation of the mobile device calculated from the received RF signals with the position and orientation information received from the sensor into a corrected position and orientation of the mobile device. 
     
     
       7. The mobile device of  claim 1 , wherein the at least one processor is further configured to restore the at least one receiver antenna to full power when the sensor detects motion. 
     
     
       8. A method of determining position of a mobile device, the method comprising:
 measuring, by a sensor, inertia of the mobile device; 
 receiving, by multiple receiver antennae of the mobile device, radiofrequency (RF) signals transmitted by at least one RF transmission source 
 calculating position information of the mobile device based on the RF signals received by the at least one receiver antenna to track the mobile device; 
 combining the calculated position information with inertial measurement data measured by the sensor to supplement the tracking of the mobile device; and 
 reducing power to the at least one receiver antenna when motion of the mobile device is not detected for a predetermined period. 
 
     
     
       9. The method of  claim 8 , further comprising the step of using a subsequent calculation of position information for the mobile device based on an inertial measurement as the position of the mobile device when the RF signals are weak, corrupted, or lost. 
     
     
       10. The method of  claim 8 , further comprising combining first position information calculated based on the inertial measurement with second position information calculated based on the received RF signals, including processing the first position information for the mobile device based on the inertial measurement in response to detecting a divergence between the first and second position information. 
     
     
       11. The method of  claim 8 , wherein the mobile device is an unmanned aerial vehicle. 
     
     
       12. The method of  claim 8 , further comprising the step of applying a filter to merge the position and orientation of the mobile device determined from the received RF signals with the position and orientation information into a corrected position and orientation of the mobile device. 
     
     
       13. The method of  claim 8 , further comprising the step of restoring the at least one receiver antenna to full power when motion of the mobile device is detected. 
     
     
       14. The method of  claim 13 , further comprising the step of keeping track of a last calculated corrected position and orientation of the mobile device and, when the motion of the mobile device is detected, to correct the last calculated position and orientation of the mobile device based on measurements made by the mobile device until the at least one receiver antenna returns to operation. 
     
     
       15. The method of  claim 8 , further comprising weighing RF data obtained from the RF signals based on a match with inertial data obtained from the measurements made by the sensor, the sensor including an inertial/magnetic devices subsystem (IMDS). 
     
     
       16. A system for tracking a position of a mobile device, the system comprising:
 a sensor attached to the mobile device, the sensor configured to determine position and orientation information of the mobile device by monitoring inertia over time; 
 a radiofrequency (RF) tracking system comprising:
 at least one RF transmitter antenna on the mobile device, 
 at least one RF receiver antenna; and 
 at least one processor in communication with the sensor and the at least one receiver antenna, the at least one processor being configured to:
 calculate position information of the mobile device based on the RF signals received by the at least one RF receiver antenna to track the mobile device; 
 compare the position information of the RF signals and the inertial measurement data to modify a position stability of the RF signals; and 
 supplementing the tracking of the mobile device by combining 
 the calculated position information with the inertial measurement data measured by the sensor; and 
 reduce power to the at least one RF antenna when motion of the mobile device is not detected for a predetermined period. 
 
 
 
     
     
       17. The system of  claim 16 , wherein the at least one processor is further configured to use a subsequent calculation of position information for the mobile device based on an inertial measurement as the position of the mobile device when the RF signals are weak, corrupted, or missing. 
     
     
       18. The system of  claim 16 , wherein the at least one processor is further configured to apply a weight to the position information based on the inertial measurement in response to detecting a divergence between first and second position information of the position information.